Patent GB-718876-A (GB)
Title: Circuit arrangement for the prevention of double testing in telecommunication installations
IPC: H04Q3/00
Filed: 1953-01-08
Abstract: 718,876. Automatic exchange systems. SIEMENS & HALSKE AKT.-GES. Jan. 8, 1953, [Jan. 10, 1952], No. 621/53. Class 40 (4). In an arrangement for preventing double connection the busying relays of the outgoing circuits normally operate more slowly than the test relays of the incoming circuits, unless two incoming circuits attempt to seize an outgoing circuit simultaneously in which case the busying relay operates first. On the initiation of a call by circuit Al relay X1 brings up G1 which operates a chain circuit for receives full current and X relapses. Relay S thereupon pulls up and switches through. If T12 is the calling party, operation of Tl brings up Al and shunts down B1 in the local connection relay set WR, so that C21 is short-circuited. Permanent loop conditions.-Contacts sp (Fig. 3) are changed over after a timed period either automatically or manually as the result of a signal to maintenance staff. Relay O1 holds up but the set WR is released. Cut-off relay TR1 remains held to the loop and busies Tll, the line affected. All intermediate lines busy.-The operation of An and R brings up Ugl over front contacts of C1, C2, .. Cn, which operates cut-off relay TRI and releases LRI. Relay TRI holds to the calling loop and engaged tone is reverted. All relay sets WR accessible to the allotted intermediate line busy.-Relays O1, 02 ... 06 will be up, so Ugl (Fig. 3) operates in series with C11, and Ug 12 with C12. Thus as soon as R comes up, C1 operates to connect up ZL2 in place of ZL1. Similarly if all relay sets available to ZL2 are busy operation of C2 connects up ZL3, and so on. 718,876. the windings (ii) of the connecting relays D11 ... D13 and assuming the outgoing circuits B2, B3 are free, relays D12, D13 operate. Relay G1 falls back followed by D13 but D12 holds over contact c2. Test relay P1 energizes in series with the holding winding (i) of relay D12 and C2. Relay P1 short circuits its high resistance winding thereby increasing the current in its circuit sufficiently to cause the holding winding D12(i) to become effective and to operate C2. The short circuiting of the high resistance winding of P1 also raises the potential of the test lead to busy the circuit B2 against seizure by another incoming circuit. If simultaneous seizure of the circuit B2 is attempted by, say, circuits A1, A2, then relay C2 receives increased current from both circuits A1, A2 in parallel and therefore operates more rapidly than either of the P relays and relays D12 D22 fall back to restore both incoming circuits whereupon each makes a further attempt. The arrangement may be used for connecting metering impulse transmitters Z, Fig. 3, to zone metering control devices V, the circuits Z corresponding to the circuits A, Fig. 1, and the circuits V to the circuits B. The arrangement is such that should dialling impulses commence before connection is established to a zone device V, none of the subsequent impulses are transmitted to the device V and busy tone is reverted. Thus if the connection is completed in time, the dialling impulses are repeated by relay A over contact 3p to the device V. If, however, P is still unoperated the first impulse operates S which locks up, disconnects the D.C. path for the impulse receiving relay A, and reverts busy tone over this relay and condense C0.